Water heaters for domestic use are commonly of two types, electric water heaters and gas-fired water heaters. With electric water heaters resistive heating elements project in the water tank and heat the water therein. With gas-fired water heaters a combustion chamber is located under the bottom wall and a gas burner is fired to heat the bottom wall and the water within the tank, Also, the flue gases from the combustion chamber extends through the tank and also heats water therein. Typically, water is heated to maintain a temperature of about 140 degrees F. When hot water is drawn from the upper region of the tank, domestic cold water under pressure is introduced in the bottom region of the tank. If for any reason the water temperature in the upper region of the tank falls the cut in setpoint of the upper thermostat, it is an indication that there is a problem with the heating devices or an over draw of hot water. Such low temperature also poses a risk that undesirable bacteria could be present as they may have proliferated in stagnant water in the bottom region of the tank and which has risen to the upper region of the tank due to an excessive draw of hot water from the upper region.
It is known that the Legionella bacteria is promoted in stagnant water. When there is no draw of hot water from a water heater the only movement of water within the tank is cause by the heating sources which causes water disturbances as hot water rises. If the heating sources are defective, and there is now draw of hot water for a long period of time, then water becomes stagnant creating dead spaces in which deposits and sediment formation can arise creating a culture medium for bacteria proliferation.
In view of the above, there is a need to provide an automatic warning system to a user person that the water temperature in the upper region of the tank is approaching a low temperature value, which may be unsafe to be exposed to, and that there may be a problem with the water heater and that the water heater will be shut-down until the water temperature in the upper region rises to a desirable safe temperature, commonly about 140 degrees F.